Use of American Mammoth Jackstock Donkeys: The Mammoth Jack’s main purpose is to produce mules for various uses. The lighter Jacks are often used to create saddle mules, while heavier boned Jacks are used for draft mules. Mammoth Jacks are also ridden and can easily carry a rider. The breed is also shown in a variety of classes at donkey shows, including donkey pleasure and harness. They also make good trail mounts.